Fringe reception and painted dish !

[horizon80]

Can any satellite boffins advise me to what extent a badly (hand )painted dish--giving 1 -2 mm of irregularity due to the paint will have on reception in a fringe area. I am in the process of trying to carefully remove the said paint, and would appreciate any recommendations which might improve the reception ,ie sanding, respraying or polishing ! Dish is 1.8 m fibreglass prime focus, and old , but I cant afford a new one!-- Reception area --Costa Blanca with usual 2d reception problems. Have just put Invacom twin lnb as recommended by a few contributors...large improvement on old lnb except for low frequencies (10714). Also what is the cause of signal loss in the evenings here... is it a slight refraction or what?..2

 

[moosegoose]

i would sand it so its smooth then lightly spray with a non metalic paint white might be a good color for hot weather.then re alinge and see what the difference is.

 

[iceman]

I don't think it will improve your reception but there are couple of points you should keep in mind..One is using a non metallic based paint as already suggested and the other is to use a matte paint...Glossy dish reflector can damage LNB plastics by focusing the sunlight certain times of the year/day

 

[PaulR]

All I can say is be careful!

A glass fibre dish is reflective to radio waves by having a metallised layer just below the surface gel coat. Don't sand away too much!

I would guess that the existing painted surface is having absolutely no effect (unless it is lead based or a metallic paint) and that you're only going to improve it visually.

As it's a prime focus dish are you using the correct type of LNB?

 

[horizon80]

Thank you for your replies, but I am now getting more confused, particularly about not using metallic paint (not that I was going to use it anyway!), as Paul says that there is a metallic layer below the gel coat to reflect the EM waves. So if there is why should you not use metallic paint.
My original thoughts were that this dish is a reflector, and this painted surface is as rough as a bears a**e. At satellite frequencies the wavelengh is extremely short, or small if you like, compared to the roughness of the surface, so is more likely to be reflected in a direction dictated to by the painted surface rather than the dish shape. Ok we know that EM waves can pass through thin paint, but we also know that they can be reflected of buildings or hills, and hills do not have a metallic layer just below the surface..do they?
The majority of thinking is to smooth the surface, and then use a non glossy paint or primer to finish . White has been suggested, but again someone quite rightly said that in the bright hot sun here( Spain), this could focus the light and heat in the lnb cover, and melt it. If a dish is a reflector, why not use glossy paint, as it will reflect more! ???...just use a darker colour. Hope this gets your grey cells thinking. ..Anyone out there into the design and building of dishes, and knows all the theory and practice ?
Keep it coming in !

 

[rolfw]

Yes, the mesh layer is below the surface, so adding a new reflective layer on the surface, will change the characteristics of the dish.

You may wish to consider using a glass fibre transparent acrylic sealant/paint after cleaning the dish, there are many available.

 

[johnsattuk]

My original thoughts were that this dish is a reflector, and this painted surface is as rough as a bears a**e. At satellite frequencies the wavelengh is extremely short, or small if you like, compared to the roughness of the surface, so is more likely to be reflected in a direction dictated to by the painted surface rather than the dish shape.

Around 20mm, would require quite a rough surface

 

[horizon80]

All I can say is be careful!

A glass fibre dish is reflective to radio waves by having a metallised layer just below the surface gel coat. Don't sand away too much!

I would guess that the existing painted surface is having absolutely no effect (unless it is lead based or a metallic paint) and that you're only going to improve it visually.

As it's a prime focus dish are you using the correct type of LNB?

Sorry, forgot to reply earlier. Yes it has prime focus lnb and new invacom twin, as suggested by this site. Interesting though an offset lnb had been fitted by a Spanish tv / sat company a year or two earlier. The original dish feedhorn was therefore missing. the invacom and new feedhorn work well, but I just need that bit more reception as I am loosing BBC/ITV at around 8pm local(7 uk)..just when the good progs are coming on ! Keep trying to re-tweak the dish, but that is as good as it gets.

 

[Robbo]

Thank you for your replies, but I am now getting more confused, particularly about not using metallic paint (not that I was going to use it anyway!), as Paul says that there is a metallic layer below the gel coat to reflect the EM waves. So if there is why should you not use metallic paint.
My original thoughts were that this dish is a reflector, and this painted surface is as rough as a bears a**e. At satellite frequencies the wavelengh is extremely short, or small if you like, compared to the roughness of the surface, so is more likely to be reflected in a direction dictated to by the painted surface rather than the dish shape. Ok we know that EM waves can pass through thin paint, but we also know that they can be reflected of buildings or hills, and hills do not have a metallic layer just below the surface..do they?
The majority of thinking is to smooth the surface, and then use a non glossy paint or primer to finish . White has been suggested, but again someone quite rightly said that in the bright hot sun here( Spain), this could focus the light and heat in the lnb cover, and melt it. If a dish is a reflector, why not use glossy paint, as it will reflect more! ???...just use a darker colour. Hope this gets your grey cells thinking. ..Anyone out there into the design and building of dishes, and knows all the theory and practice ?
Keep it coming in !

The EM waves would pass through a layer or two of non-matallic paint as if it is not there I believe. But buildings and hills etc are a different matter. Moisture content is probably a major factor.

 

[Analoguesat]

Sorry, forgot to reply earlier. Yes it has prime focus lnb and new invacom twin, as suggested by this site. Interesting though an offset lnb had been fitted by a Spanish tv / sat company a year or two earlier. The original dish feedhorn was therefore missing. the invacom and new feedhorn work well, but I just need that bit more reception as I am loosing BBC/ITV at around 8pm local(7 uk)..just when the good progs are coming on ! Keep trying to re-tweak the dish, but that is as good as it gets.

1.8m is too small for good 2D reception in the Costa Blanca - you need about 2.4m for perfect reception

 

[horizon80]

You are quite right, it does need a 2.5 m, ot larger dish, but this is mother's dish, and mother's home, and as she does not watch tv, does not want it changing!!! Now you know the problem! Anyway I like a challenge, and don't like to be beaten, so I am trying every trick in the book to get a marginal improvement here and there. No one has asked me about focusing or skew yet. Done that...focusing is not as critical as I might have expected... seems to be Ok for +- 4 mm...is this normal? I don't know if it is a change in atmotspheric conditions or paint removal, but there has been some improvement so far.